Galactosamine is a well-known hepatotoxin that causes a diffuse focal hepatic necrosis. The appearance of the hepatic lesion has long been linked to depletion of cellular UTP stores; however depletion of glutathione and a late-phase rescue by sulfhydryl compounds are also observed. Furthermore, activation of Kupffer cells can enhance galactosamine hepatotoxicity. Since activated macrophages secrete active oxygen and glutathione is well-known cellular reductant, it is possible that oxidative stress may be contribute to galactosamine toxicity by increasing the exposure of the compromised cells to active oxygen species. An alternate hypothesis is that macrophages secrete humoral factors that act through specific cellular receptors to decrease the ability of the cell to resist toxic injury. We have developed a primary rat hepatocyte culture system that shows the major features of in vivo galactosmaine hepatotoxicity, UTP depletion that is reversible by uridine, and suppression of glutathione resynthesis. Of importance, preliminary studies have shown that galactosamine toxicity to hepatocytes is enhanced when the cells are cocultured with activated macrophages. We believe that we have an ex vivo experimental system that will allow us to determine whether macrophages exacerbate galactosamine toxicity through the release of active oxygen species or through the release of humoral factors. The long-term goal of this research is to elucidate the mechanism of galactosamine-induced hepatic necrosis. The objectives of the present studies are to a) characterize the exacerbating effect of activated macrophages on galactosamine toxicity in hepatocyte cultures, b) examine the roles of active oxygen species and humoral factors in the exacerbation of galactosamine (or its metabolites), and d) to examine the effect of modulation of glutathione levels on galactosamine toxicity in the hepatocyte cultures.